Systems and methods for non-destructive mass sensing

ABSTRACT

The invention provides systems and methods for measuring the mass of a substance. In one method, energy is applied to a substance and a response resulting from the application of energy as measured. The mass of the substance is then determined based at least in part on the measured response.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 11/999,316 filed on Dec.4, 2007, which is a continuation of application Ser. No. 09/731,317(U.S. Pat. No. 7,304,750) filed on Dec. 6, 2000, which claims thebenefit of U.S. Provisional Application No. 60/172,316 filed Dec. 17,1999, the entire disclosures of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of measuring, and inparticular to the field of mass measurement. More specifically, theinvention relates to techniques for measuring the mass of a substancethat has been volumetrically metered.

In many fields, there is a need to precisely measure the mass of asubstance. For example, substances such as drugs, chemicals, and thelike may often need to have their mass measured. For instance, drugs areoften prescribed in terms of unit dosages that are often determinedbased on the mass of the drug formulation. Therefore, the mass of thedrug formulation contained in such unit dosages needs to be measured.

A traditional way to measure the mass of a substance is by use of abalance or a scale. Although effective in precisely measuring the massof a substance, such techniques can be inefficient for commercialproduction of a product, such as when producing large volumes of unitdrug dosages. For example, some unit dosages of drugs consist of agranular of powder drug formulation stored in receptacles, such asblister packs, capsules, caplets, or the like. To test whether thereceptacle includes a unit mass of the drug formulation, the receptacleis opened and the powder is removed and weighed. Because of thedestructive nature of the test, only periodic samplings are typicallyperformed.

For some types of substances, a convenient way to meter isvolumetrically. For example, substances such as powders, granularsubstances, and the like are easily measured by filling a known volumewith the substance. However, merely filling a known volume with asubstance does not guarantee that the metered substance has a knownmass. For example, when volumetrically metering the substance, thedensity of the substance may change due to packing conditions, voidswithin the substance, and the like. Hence, in cases where the mass ofthe substance needs to be metered, volumetric metering may not guaranteean accurate result.

Hence, the invention is related to techniques for measuring the mass ofa substance, and particularly the mass of a substance that has beenvolumetrically metered. In this way, the invention provides techniquesfor measuring the mass of a substance in a high throughput manner.

SUMMARY OF THE INVENTION

The invention provides exemplary systems and methods for measuring themass of the substance. According to one method, the mass is measured byapplying energy to the substance and measuring a response resulting fromthe application of energy. The mass of the substance is then determinedbased on the measured response.

In one aspect, the substance is volumetrically metered prior to applyingthe energy. For example, the substance may comprise a powder that ismetered by depositing the powder within a metering chamber. Tofacilitate metering, a vacuum may be drawn through the metering chamberto assist in capturing falling powder into the chamber.

A variety of techniques may be employed to apply energy to thesubstance. For example, electromagnetic radiation may be directed ontothe substance. Conveniently, the electromagnetic radiation may compriselight that is directed onto the substance. Light that is transmittedthrough the substance or emitted from the substance may then bemeasured, and the mass determined by correlating the amount of measuredlight with an associated mass. In some cases, the transmitted or emittedlight may create an interference pattern with the light being directedonto the substance. Such an interference pattern may be measured andcorrelated with an associated mass.

As another alternative, the energy applying step may comprise applyingelectrical current of a voltage to the substance. The impedance of thesubstance may then be measured and correlated with an associated mass.As another alternative, vibrational energy may be applied to thesubstance and the amount of energy dissipation caused by the substancemay be measured. For example, a piezo electric element may be vibratedabove the substance to subject the substance to pressure changes. Thevibrational frequency of the piezo electric element may then be measuredafter energy has been dissipated by the substance. The measuredvibrational frequency may then be compared with a natural oscillatingfrequency of the piezo electric element, and the change in frequencycorrelated with an associated mass.

In another aspect of the method, the determined mass may be comparedwith a range of masses that defines an acceptable unit mass range. Inthis way, a test is provided to rapidly determine whether the measuredsubstance is within an acceptable range. This information may then beused, for example, to alter the manner in which the substance is beingdeposited within a metering chamber so that the mass will fall withinthe acceptable range. For example, when a vacuum is employed to drawpowder into a chamber, the amount of vacuum and/or the rate at which thepowder is permitted to fall may be varied in a subsequent fillingoperation based on the measured mass in comparison to the acceptablerange.

In another specific aspect, the metering chamber may be included withina rotatable drum that is rotated between multiple positions whendepositing powder within the chamber and when measuring the mass of thepowder. After the mass has been measured, the drum may be rotated toanother position and the powder ejected from the chamber and into areceptacle. In this way, the drum may be continuously rotated betweenthe various positions to deposit a mass of powder into the chamber, tomeasure the mass of the metered powder, and to eject the powder into areceptacle.

The invention further provides an exemplary system for measuring themass of a substance. The system comprises a metering chamber thatdefines a certain volume for receiving a substance. An energy source ispositioned to supply energy to the substance when within the meteringchamber. At least one sensor is provided to measure a response from thesubstance due to the application of energy from the energy source. Aprocessor is coupled to the sensor to determine a mass of the substancewithin the metering chamber based at least in part on the measuredresponse.

In one aspect, the energy source comprises a source of electromagneticradiation disposed to direct electromagnetic radiation onto thesubstance. Conveniently, the sensor may comprise a radiometer or areflectometer to detect the amount of transmitted or emitted light fromthe substance. The processor may then be employed to determine the massof the substance by correlating the amount of transmitted or emittedlight with a stored mass value. Conveniently, the loss of transmittedlight may be computed by comparing an intensity value of a beam ofradiation after passing through the substance with an intensity value ofa beam from the radiation source that passes through the chamber in theabsence of the substance. In one particular aspect, the metering chambermay include a filter at a bottom end upon which the substance rests. Theradiation source may be configured to pass a beam through the filter andthen through the chamber.

In another particular aspect, the sensor may be configured to measure aninterference pattern that is caused by the transmitted or emitted lightthat interferes with the light being directed onto the substance. Theprocessor may then be configured to determine the mass of the substanceby correlating the measured interference pattern with an associatedmass.

As another alternative, the energy source may comprise an electrode thatis positioned to pass electrical current or a voltage to the substance.With such a configuration, the sensor may comprise a sensing electrodeand circuitry to measure the capacitance of the substance. As analternative, the energy source may comprise a vibratable element forapplying vibrational energy to the substance. The sensor may beconfigured to measure an amount of energy dissipated by the substance.For example, the vibratable element may comprise a piezo electricelement for supplying pressurized air pulses to the substance. Thesensor may then comprise circuitry to determine the vibrationalfrequency of the piezo electric element after energy has been dissipatedby the substance. The processor may be configured to compare themeasured vibrational frequency with a natural oscillating frequency ofthe piezo electric element, and to correlate the change in frequencywith an associated mass.

In another specific aspect, a vacuum source may be placed incommunication with the chamber to assist in drawing the substance intothe chamber. Further, the chamber may be disposed within a rotatabledrum. In this way, the drum may be placed at a filling position wherethe substance is deposited into the metering chamber. The drum may thenbe rotated to a station where the mass is metered. Finally, the drum maybe rotated to a dispensing position where the metered powder is ejected.Advantageously, the processor may be configured to compare thedetermined mass of the substance with a range of acceptable mass values.Depending on the outcome of the comparison, the processor may includecode to alter the amount of vacuum and/or operation of a fluidizationapparatus that fluidizes the substance before being deposited within themetering chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the variance of the mass of a substancethat is volumetrically metered over time.

FIG. 2 a is a graph illustrating the relationship between a measuredsignal intensity and a fill mass deviation according to the invention.

FIG. 2 b is another graph illustrating the relationship between ameasured signal intensity and a fill mass deviation according to theinvention.

FIG. 3 is a schematic side view of a mass measuring system using asource of electromagnetic radiation.

FIG. 4 is a schematic side view of an alternative mass measuring systemutilizing the principal of optical coherence interferometry to measurethe mass.

FIG. 5 is a schematic side view of another alternative mass measuringsystem which uses optical coherence interferometry to measure the mass.

FIG. 6 is a schematic side view of a mass measuring system whichmeasures capacitance to determine the mass of a substance.

FIG. 7 is a schematic side view of an electromechanical resonant massmeasuring system utilizing a piezo electric element.

FIG. 8 is a schematic side view of a mass measuring system having anenergy source and detector integrated into a metering chamber.

FIGS. 9-11 illustrate top schematic views of other embodiments ofmetering chambers having different arrangements of energy sources anddetectors for measuring the mass of a substance within the meteringchamber according to the invention.

FIG. 12 is a flow chart illustrating one method for measuring the massof a substance according to the invention.

FIG. 13 is a schematic side view of a powder filling system thatincludes components for sensing the mass of a metered substanceaccording to the invention.

FIG. 14 is a more detailed view of a metering chamber of the system ofFIG. 13.

FIG. 15 is a perspective schematic view of the system of FIG. 13.

FIG. 16 is a schematic view of an alternative system for measuring themass of a substance according to the invention.

FIG. 17 is a graph illustrating the relationship between lighttransmitted through various powder pucks and their associated massaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides exemplary systems and methods for measuring themass of a substance in a non-destructive manner. The systems and methodsmay be employed to measure a specific mass or simply to indicate whethera given sample has an acceptable mass. In this way, the masses ofsamples that are metered in a continuous process may be measured at thetime of metering so that unacceptable samples are not continuouslyproduced until the next periodic sampling. For example, as illustratedin the graph of FIG. 1, a metering process may be employed to meter agiven substance into unit samples over time using a metering chamber. Attime T₁, the system is calibrated so that the first sample does notdeviate from an acceptable unit mass. However, over time the meteredsamples have a mass that deviates from the baseline mass. At time T₂,the metered sample exceeds a specified range and is therefore consideredunacceptable. Hence, if the manner in which the substance is metered isnot varied at time T₂, the metered samples may continue to beunacceptable until time T₃ where one of the samples is removed from itspackage and measured to discover its unacceptable mass. At this point,the system may be readjusted. However, a number of unacceptable sampleswill need to be discarded. For example, it may be necessary to discardall the samples produced since the last calibration or comparison, i.e.all samples produced between T₁ to T₃.

According to the invention, the mass of each sample may be evaluated atthe time of filling and in a non-destructive manner so that when one ofthe samples becomes unacceptable, an error condition may be produced toindicate that the system needs to be readjusted. By non-destructivelymeasuring the mass of each sample, the samples produced between T₂ andT₃ do not need to be discarded. Rather, the system may be readjusted sothat the samples again fall within the acceptable range as shown. Theability to non-destructively sense the mass is useful when the meteredsamples are placed within receptacles or containers that must bedestroyed to extract the samples and weigh the samples usingconventional techniques. With the invention, sampling may occur often,e.g. after each sample has been metered, rather than only periodicallyas is common with destructive mass tests.

The invention may be utilized to measure the mass of a wide variety ofsubstances. Merely by way of example, such substances may includepowders, including powders having pharmaceutical agents and/or otherpharmaceutically acceptable excipients and that have a mass mediandiameter in the range from about 0.1 μm to about 100 μm, granularsubstances, and the like. To facilitate measurement of the mass of suchsubstances, the substances may initially be volumetrically metered, suchas in a metering chamber. Non-limiting examples of systems andtechniques for metering powered substances are described in U.S. Pat.No. 5,826,633 and co-pending U.S. application Ser. No. 09/312,434, filedMay 14, 1999, the complete disclosures of which are herein incorporatedby reference. However, it will be appreciated that the invention is notlimited to measuring the mass of substances that have been metered insuch a manner.

To measure the mass of a metered substance, some form of energy isapplied to the substance and a response is measured. The energy may beapplied while the substance is within a metering chamber, or after ithas been removed from a metering chamber, including while the substanceis traveling through the air after being expelled from the meteringchamber. The measured response is then compared to empirical data todetermine an associated mass, either in absolute terms or in relativeterms, e.g. a deviation from an acceptable value. Hence, the inventionalso encompasses the creation of empirical data showing a relationshipbetween measured responses created by the application of energy andassociated masses that have been measured using conventional techniques.Merely by way of example, a beam of light may be shined onto a meteredamount of a substance and the loss of transmitted light measured. Themetered substance may then be placed onto a scale and weighed todetermine the mass. Another sample of the substance may then be meteredunder different conditions to vary the packing density. Light is shinedonto the second substance and the loss of transmitted light measured andstored. The sample is then weighed and associated with the measuredtransmission value. This process is repeated until a sufficient numberof values have been obtained to adequately define a relationship betweenmeasured signals and associated masses for a desirable mass range.

Examples of how empirical data may appear when plotted are illustratedin the graphs of FIGS. 2 a and 2 b. In one aspect, the response curvemay vary nearly linearly with fill mass over a certain dynamic range.Because of the limitations of some measurement systems, the linearregion may deviate at either end due to conditions such as thresholdingand saturation (see FIG. 2 b). These and other effects may be the resultof the measuring equipment or instrumentation. However, even if theresponse curve is not linear it may still be useful if it is wellcharacterized and repeatable.

In FIG. 2 a, the response curve was generated from transmission data,e.g., light. In FIG. 2 b, the response curve was generated usingfluorescence and interferometry. Both response curves utilize arbitraryunits for signal intensity. Hence, with the examples of FIGS. 2 a and 2b, the mass of a metered sample may be determined by subjecting thesubstance to some form of energy and measuring a appropriate response.Using the information available from the response curve, the measuredresponse is associated with a mass, either in relative terms or as adeviation from a baseline value as shown in FIGS. 2 a and 2 b.

A wide variety of energy forms may be applied to the substance tomeasure its mass. Similarly, a wide variety of sensors may be employedto sense and measure the response. For example, types of energy that maybe employed include electromagnetic radiation energy, includingradiation in the ultraviolet, visible, infrared, millimeter wave andmicrowave spectra, electrical energy, mechanical energy, includingvibrational energy, and the like. A variety of sensing modalities mayalso be employed including infrared transmission, capacitance, x-raydefraction, beta decay attenuation, and the like.

Electromagnetic radiation may be employed to interact with the substancethrough diverse phenomena which may then be correlated with the mass ofthe powder. Such phenomena include, for example, absorption, scattering,fluorescence and interference. These phenomena may span a wide spectrumof wavelengths, including ultraviolet, visible, infrared, millimeterwave, and microwave as previously described. Once a phenomenon ofinterest has been specified within a wavelength band, various approachesmay then be employed to implement the phenomenon of interest. Forexample, electromagnetic radiation may propagate freely, e.g. usinglenses and antenna, or be constrained as a guide wave, e.g. withinoptical fibers, planar integrated structures, microstrip circuits, otherconduits, and the like. Further, the measurand may be transduced in avariety of ways, including the use of a single detector, video imaging,synthetic aperture techniques, and the like. Processing the signal mayinvolve synchronous detection, averaging, adaptive filtering, tomographyand the like.

Referring now to FIG. 3, one embodiment of a mass measuring system 10will be described. System 10 comprises a change tool 12 that forms ametering chamber 14. Disposed below metering chamber 14 are a set offilters 16. Change tool 12 is particularly useful with a powder fillingsystem where air or other gases are drawn through metering chamber 14 tocapture fluidized powder within metering chamber 14 in a manner similarto that described in U.S. Pat. No. 5,826,633 and co-pending U.S. patentapplication Ser. No. 09/312,434, filed May 14, 1999, previouslyincorporated by reference. However, it will be appreciated that system10 may be used in connection with essentially any type of meteringchamber, and is not limited to metering chambers formed within specificchange tools.

As shown in FIG. 3, once metering chamber 14 has been filled with powderthe powder forms a puck 18, i.e. a loosely packed tablet. Disposed onone side of change tool 12 is a light source 20 for directing light ontoa surface of puck 18 as shown. Although light source 20 is shown on theside of change tool 12 having filter 16, it will be appreciated thatlight source 20 may be used on the other side of change tool 12 as well.Positioned to detect light from puck 18 is a detector 22.

System 10 may be employed in one of two modes. First, detector 22 may beconfigured to detect the loss of transmitted light or the stimulation offluorescence. With either approach, light source 22 is positioned todirect light toward one side of puck 18 while detector 22 is positionedon the other side of puck 18 to intercept the available light. Whendetecting the loss of transmitted light, the detected light is of thesame wavelength as is produced by source 20. With the stimulation offluorescence, the detected light is of a longer wavelength than producedby source 20. The light from source 20 may be focused, collimated, ordivergent. Further, the light may be modulated, pulsed or continuous. Asanother option, the spectral distribution may be narrow or broad band,optionally with a characteristic signature. Further, the light emissionsmay be incoherent or possess some coherence length.

Detector 22 may be configured to have a spectral response adequate fordetection of the light impinging on its surface. Detector 22 may beoperated at room temperature or may be cooled. Further, detector 22 mayoptionally incorporate some amplification electronics. Both source 20and detector 22 may include various optical elements, such as lenses,wavelength filters, spatial filters, optical fibers, and associatedmounting hardware.

In one specific embodiment, detector 22 may comprise a silicon detectorradiometer. For instance, one type of radiometer that may be employed isModel No. IL1700, from International Light. Light source 20 may comprisea laser, such as a 5 mW, 630 nm, laser, commercial available fromCoherent.

Hence, with system 10 the mass of puck 18 may be determined simply bymeasuring the loss of transmitted light or the stimulation offluorescence when light from source 20 is shined onto puck 18. Themeasured light or fluorescence may then be associated with acorresponding mass using a pre-defined empirical relationship in amanner similar to that previously described.

FIG. 4 illustrates an alternative mass measuring system 24 that utilizesa change tool 26 that defines a metering chamber 28 and includes afilter 30 similar to the embodiment of FIG. 3 as previously described.Metering chamber 28 is filled with a powder puck 32. System 24 furtherincludes a combined light source/detector 34 that is employed to directlight onto powder puck 32 as shown by the arrows. The detector may thenbe employed to detect the reflection of light or the stimulation offluorescence. With either approach, at least a portion of the puck'svolume beneath the surface is involved in producing the reflected lightor the stimulation of fluorescence. For example, the light source may beconfigured so that the light penetrates a certain distance into puck 32in order to profile the packing density of puck 32. Below this distance,the mass variation of the powder is assumed to be constant. Hence, onlya top portion of the puck needs to be evaluated to determine whether themass of puck 32 will vary beyond an acceptable range. Conveniently,light source/detector 34 may be configured such that the light sourceand detector share some or all of the same optical elements.

The light source and detector of system 24 may be employed to measurethe mass of puck 32 in a manner similar to light source 20 and detector22 of system 10 as previously described. Alternatively, system 24 may beconfigured to measure the mass using optical coherence interferometryusing one common optical fiber for both source and detector optics. Thistechnique permits the packing density of puck 32 to be profiled within aregion beneath the surface of puck 32 based on interference patternsgenerated by the interference of the reflected or fluorescent light withthe light being directed onto the surface of puck 32.

In one specific embodiment, a precision reflectometer may be employed tomeasure light from puck 28. One specific reflectometer that may be usedis Model No. HP8504B, commercially available from Agilent.

As shown in FIG. 5, system 24 may be modified to include a light source36 that is separate from a detector 38. Source 36 and detector 38 aredirected toward the same face of puck 40 at an angle to optimizedetection. Detector 38 may be employed to measure reflected light,fluorescent light or interference patterns as previously described.

Some of the substances utilized by the invention, such as powders, maybe dielectric in nature. As such, the capacitance of a circuit thatincludes a metered amount of a substance may be employed to determinethe mass of the substance. Conveniently, the metering chamber may beformed of a conducting material which may form one electrode in thecircuit.

One specific example of a mass measuring system 42 for measuringimpedance or capacitance is illustrated in FIG. 6. System 42 comprises achange tool 44 defining a metering chamber 46 and including filters 48in a manner similar to that described with previous embodiments. Asshown, chamber 46 is filled with a powder puck 50 that is dielectric innature. Change tool 44 is constructed of a conductive material andserves as one electrode. A sensing electrode 52 is also provided, withchange tool 44 and sensing electrode 52 forming the plates of acapacitor. Change tool 44 may be passively tied to ground potential orit may be driven to a potential using a reference electrode drive 54.The potential may be any value, including ground potential. System 42further includes a guard electrode 56 and a guard drive 58 to serve asan electric shield. The detection electronics may be single ended or maybe an impedance bridge 60, with the puck capacitor as one element of abridge arm. In this way, when the electrodes are energized, thecapacitance or impedance of puck 50 may be determined. The measuredresponse may then be correlated with an associated mass in a mannersimilar to that previously described.

In one specific embodiment, a dielectric analyzer may be employed whenmeasuring the capacitance of system 42. For example, one type ofdielectric analyzer that may be employed is Model No. HP4291B,commercially available from Hewlett Packard.

Another technique for measuring the mass of a substance is to provide atuned mechanical or electromechanical system whose resonance conditionis affected by changes in its mass. An increase in mass coupled to aresonant electromechanical system may result in an increase in energydissipation and a dampening of the resonant condition. The resonantfrequency may also be affected. Any of these events may be detected andemployed to determine the mass of the substance included within thesystem.

One non-limiting example of such an electromechanical resonance system62 is illustrated in FIG. 7. System 62 includes a change tool 64 thatdefines a metering chamber 66 and includes a filter 68 similar to otherembodiments. A powder puck 70 is disposed within chamber 66. Rigidlyaffixed to change tool 64 is a piezo electric element 72. When powderpuck 70 fills metering chamber 66, a column of air is sealed betweenpuck 70 and piezo electric element 72. An electronic bridge 74 may beemployed to actuate vibration of piezo electric element 72 to providepressure pulses to the surface of puck 70. In some cases, piezo electricelement 72 may also vibrate change tool 64. Without puck 70, piezoelectric element 72 vibrates at a natural harmonic frequency. When puck70 fills metering chamber 66, piezo electric element 72 vibrates at adifferent frequency. This change may be detected by electronic bridge 74and used to correlate an associated mass in a manner similar to thatpreviously described.

Any of the energy sources and/or detectors as described herein may beconstructed to be intregally formed within a change tool or otherstructure that forms the metering chamber. Such an example isillustrated schematically in FIG. 8 where a change tool 76 is shown.Change tool 76 defines a metering chamber 78 and includes filters 80similar to other embodiments. A powder puck 82 fills chamber 78. Formedabout the walls of chamber 78 is a source and/or detector element 84.Element 84 is representative of any of the sources, detectors, and/orelectronics as previously described in connection with the otherembodiments. As shown in FIG. 9, element 84 may comprise a singlediscrete element. FIG. 10 illustrates element 84 as an array of elementssuitable for dielectric or optical tomography, and FIG. 11 illustrateselement 84 as a continuous annular element. In this way, the amount ofspace required when constructing a mass measuring system may besignificantly reduced.

Referring now to FIG. 12, one method that may be utilized to measure themass of a substance will be described. Initially, a mass measuringsystem is calibrated as shown in step 86. The manner in which the systemis calibrated depends upon the particular sensors and/or detectors beingemployed. For example, when directing light through the substance toperform the mass measurement, the system may be calibrated by directinglight through the metering chamber when the metering chamber is empty.This measurement may then be used as a baseline value. As shown in step88, the chamber is then filled with powder so that a metered volume ofpowder is within the chamber. Energy is then applied to the powder asillustrated in step 90, and a response is measured as shown in step 92.The mass is then determined based on the measured response as shown instep 94. As previously described, this may be accomplished by referringto empirical data. Optionally, the powder may then be ejected into areceptacle as shown in step 96. The method then proceeds to step 98where a determination is made as to whether more receptacles are to befilled. If none are left to be filled, the process ends at step 100. Ifmore are to be filled, the process proceeds to step 102 where themeasured mass is compared with a range of acceptable masses to determinewhether the measured mass of the ejected powder is within an acceptablerange. If not, the process proceeds to step 104 where fill parameters ofthe system may be varied. Optionally, a flag may also be provided toapprise the operator of the unacceptable mass. The process then revertsback to step 86 where the system is recalibrated and continues aspreviously described.

The mass measuring systems and techniques of the invention may beemployed with essentially any type of metering system. Merely by way ofexample, one type of metering system 106 that may be used with thetechniques of the invention is illustrated in FIG. 13. Metering system106 is similar in some aspects to the powder filling systems describedin U.S. Pat. No. 5,826,633 and co-pending U.S. application Ser. No.09/312,434, previously incorporated by reference. As also shown in FIG.15, metering system 106 includes a rotatable drum 108 that includes achange tool 110 having a plurality of metering chambers 112. Disposedbelow metering chambers 112 are a pair of filters 114 and 116 as bestillustrated in FIG. 14. A manifold 118 is positioned between meteringchambers 112 and serves as a conduit for a vacuum and/or pressurized airwhen filling metering chambers 112 with powder or ejecting the meteredpowder pucks from metering chambers 112 and into cavities 120.Receptacles or blister packs may be formed by enclosing cavities 120 asis known in the art.

As shown in FIG. 15, positioned above rotatable drum 108 is a hopper 122for holding an amount of powder 124. A vibratable element 126 isconfigured to move within hopper 122 while vibrating to fluidize powder124 and to assist its introduction into chambers 112. Following fillingof chambers 112, rotatable drum 108 is rotated so that a doctor blade128 may scrape off any excess powder extending above metering chambers112. Rotatable drum 108 may be further rotated so that metering chambers112 are aligned with cavities 120 to permit the metered powder to beejected into cavities 120.

A motor 130 is employed to rotate rotatable drum 108. A controller 132is coupled to motor 130 to control operation of motor 130. Thecontroller 132 is also coupled to vibratable element 126 to control bothits translation within hopper 122 as well as the frequency of vibration.A vacuum/pressure source 134 is also coupled to controller 132 and torotatable drum 108 to supply the vacuum and/or positive pressure asappropriate.

System 106 further includes a pair sensors 136 and 138. Included withinrotatable drum 108 are a series of optical fibers 140 that are eachaligned with one of the metering chambers. The controller is alsoemployed to control a light source which supplies light to opticalfibers 140 and to control operation of sensors 136 and 138.

With such a configuration, rotatable drum 108 may be moved so thatmetering chambers 112 are aligned with sensors 136. Light may then beshined through optical fibers 140 and detected by sensors 136 whilecavities 112 are empty of powder. This measurement then serves as thecalibrating or baseline measurement. Rotatable drum 108 may then bemoved to align metering chambers 112 with hopper 122. Vibratable element126 may then be actuated to fill metering chambers 112 with powder aspreviously described. Rotatable drum 108 is then moved to align thefilled chambers 112 with sensors 138. Light is then shined throughoptical fibers 140 and a measurement is taken with sensors 138. Thecontroller may then be configured to determine the loss of lighttransmission and/or fluorescence and associate this value with acorresponding mass value. The controller may also be configured todetermine whether this value is within an acceptable range.

Optionally, the controller may be configured to vary certain parametersof system 106 if the mass is not within an acceptable range. Forexample, the controller may control the rate of translation or thefrequency of vibration of vibratable element 126. The controller mayalso be configured to vary the vacuum drawn through metering chambers112 when being filled. Hence, after each filling operation, the mass ofthe metered powder puck may be evaluated and the system may be alteredto ensure that the metered powder remains within acceptable ranges.

The mass of a metered substance may also be measured after being ejectedfrom a metering chamber. FIG. 16 illustrates a system 150 that may beused to measure the mass of a puck 152 after it has been metered withina metering chamber 154. In FIG. 16, puck 152 has been ejected frommetering chamber 154 and is traveling through the air toward areceptacle 156. An energy source 158 is employed to direct energy ontopuck 152 and a sensor 160 is employed to sense a response using any ofthe techniques previously described herein, including, for example,dielectric capacitance, optical, or fluorescence. Based on the measuredresponse, an associated mass may be determined in a manner similar tothat previously described herein.

EXPERIMENTAL

The following is one non-limiting example of a technique that may beemployed to determine a relationship between light transmitted throughpowder pucks and their associated masses. In this example, a systemsimilar to the system of FIG. 3 (without the use of filter 16) wasemployed. Initially, a powder puck was manually placed into a meteringchamber of fixed volume within a change tool. The change tool was heldhorizontally such that the wide portion of the metering chamber facedupwards. Powder was introduced into the metering chamber with a spatulawhile a slight vacuum was applied to the back of the metering chamber.The vacuum served to compress the powder into a formed puck.

After forming the puck, the change tool was placed in a rigid fixture. Alaser (630 nm, 5 mW, Coherent) was positioned so that its beam wasperpendicular with the change tool and was centered on the meteringchamber. The laser beam cross section was essentially circular and ofsufficient diameter to completely illuminate the back of the meteringchamber. A silicon detector was positioned near the wide face of themetering chamber so as to receive the transmitted laser light. Thedetector's face was parallel to the change tool and concentric with themetering chamber. The detector's response was recorded with a radiometer(IL1700, International Light).

The change tool was then removed from the fixture and a slight positivepressure was applied to the back of the metering chamber in order toeject the puck into a weigh boat resting on a microbalance (MT-05,Mettler-Toledo). The mass of the puck was recorded as an increase fromthe mass of the weigh boat. This procedure was repeated for severalpucks to obtain a relationship between transmitted light and puck mass,as shown in FIG. 17.

The invention has now been described in detail for purposes of clarityof understanding. However, it would be appreciated that certain changesand modifications may be practiced within the scope of the appendedclaims.

1. A method for measuring the mass of a powder substance, the methodcomprising: applying energy to a powder substance, wherein the powdersubstance comprises particles; measuring a response resulting from theapplication of energy; determining the mass of the powder substancebased on the measured response; and ejecting the powder substance into areceptacle.
 2. A method as in claim 1, wherein the receptacle is ablister.
 3. A method as in claim 1, wherein the receptacle is a capsule.4. A method as in claim 1, further comprising volumetrically meteringthe powder substance prior to applying the energy.
 5. A method as inclaim 4, wherein the metering step comprises depositing the powdersubstance within a metering chamber.
 6. A method as in claim 5, whereina vacuum is applied to the metering chamber during the depositing of thepowder substance within the metering chamber.
 7. A method as in claim 5,wherein the powder substance is deposited within the metering chamberfrom a hopper positioned above the metering chamber.
 8. A method as inclaim 7, wherein a vibratable element is provided within the hopper toassist in depositing the powder substance within the metering chamber.9. A method as in claim 5, wherein the metering chamber is in arotatable drum.
 10. A method as in claim 1, wherein the energy applyingstep comprises directing electromagnetic radiation onto the powdersubstance.
 11. A method as in claim 1, wherein the energy applying stepcomprises directing light onto the powder substance.
 12. A method as inclaim 11, wherein the measuring step comprises measuring lighttransmitted through the powder substance, and wherein the determiningstep comprises correlating the measured light with an associated mass.13. A method as in claim 11, wherein the measuring step comprisesmeasuring light emitted from the powder substance, and wherein thedetermining step comprises correlating the measured light with anassociated mass.
 14. A method as in claim 11, wherein the measuring stepcomprises measuring an interference pattern caused by transmitted oremitted light from the powder substance interfering with the lightdirected onto the powder substance, and wherein the determining stepcomprises correlating the interference pattern with an associated mass.15. A method as in claim 1, wherein the energy applying step comprisesapplying current or voltage to the powder substance, wherein themeasuring step comprises measuring an impedance or a capacitance, orboth of the powder substance, and wherein the determining step comprisescorrelating the impedance or a capacitance, or both with an associatedmass.
 16. A method as in claim 1, wherein the energy applying stepcomprises applying vibrational energy to the powder substance, andwherein the measuring step comprises measuring an energy dissipationcaused by the powder substance.
 17. A method as in claim 16, wherein thestep of applying vibrational energy comprises vibrating a piezoelectricelement to subject the powder substance to pressure changes, wherein themeasuring step comprises measuring the vibrational frequency of thepiezoelectric element after energy has been dissipated by the powdersubstance, and wherein the determining step comprises comparing themeasured vibrational frequency with a natural oscillating frequency ofthe piezoelectric element, and correlating the change in frequency withan associated mass.
 18. A method as in claim 1, further comprisingcomparing the determined mass with a range of masses that defines anacceptable unit mass range to determine whether the measured powdersubstance is within the acceptable range.
 19. A method as in claim 1,further comprising processing the response using tomography.